The present invention relates to an electromagnetic relay for use as a small electromagnetic relay that can be mounted on a printed-circuit board, for example.
In general, this kind of small electromagnetic relay has the following structure. Specifically, the electromagnetic relay includes a resin spool having flange portions formed at both sides of its cylindrical portion. The spool has coils wound thereat to form a coil assembly. The spool has an iron core inserted into its central axis position. The iron core exposes its head portion from the flange portion and this head portion serves as a portion to magnetically attract an armature by an electromagnet.
A yoke is shaped like a plate portion having a length nearly equal to the length of the spool in the axial direction. This yoke is attached to the spool in such state in which it may extend to the flange portions of both sides of the spool. The yoke has a movable contact spring attached to its plate portion. This movable contact spring is shaped at its flange portion side in which the head portion of the iron core is located such that it may be bent in the direction nearly perpendicular to the yoke. An armature made of a square steel plate is attached to the movable contact spring at it surface side in which its bent portion oppose the head portion of the iron core. Further, the movable contact spring includes a portion projecting to the direction parallel to the plate surface direction of the armature, and this projecting portion has a movable contact formed thereon.
A break (i.e., normally closed) fixed contact terminal and a make (i.e., normally open) fixed contact terminal are narrow L-like plates having predetermined widths and a break contact and a make contact are provided at tip end portions of the L-like plates. The break fixed contact terminal and the make fixed contact terminal are fitted into the grooves formed at the flange portion of the spool with pressure and thereby attached.
In the case of the conventional electromagnetic relay having the above-mentioned structure, since the break fixed contact terminal and the make fixed contact terminal are directly fixed to the resin spool, there is a risk that the following problems arise.
Specifically, while a drive current is flowing through the coils of the electromagnetic relay, when the movable contact and the make contact are connected and an excess current flows through the movable contact and the make contact due to an accident, the drive current causes the coils to generate heat and conductor portions such as the movable contact spring and the fixed contact terminal generate heat. When the coil and the conductor portions generate heat, the heat thus generated fuses the resin spool. When the resin spool is fused by heat, there occurs an abnormal state in which the movable contact and the make contact are fixed in the xe2x80x9cON modexe2x80x9d which is the connected state.
Thereafter, even when an interlayer short circuit (i.e., so-called coil layer short) occurs in the coil, the movable contact does not return to the break contact side and the movable contact is still connected to the make contact.
If the mode of the electromagnetic relay is xe2x80x9cON modexe2x80x9d when such trouble occurred in the electromagnetic relay, then an excess current continues to flow through the make contact, There is then a risk that other trouble will occur.
In the case of the above conventional electromagnetic relay, the break fixed contact terminal and the make fixed contact terminal are fitted into the grooves of the flange portions of the spool with pressure. When the break fixed contact terminal and the make fixed contact terminal are fitted into the grooves with pressure, the fixed contact terminals made of made of copper alloys cut the resin spool to produce shavings, and shavings are scattered around the fixed contact terminals. Contact sets of the movable contact, the break contact and the make contact exist near the pressure engagement portions (i.e. groove portions formed at the flange portions of the spool). Since scattered shavings lie between these contacts, there is a risk that a trouble of contact failure will occur between these contacts.
As an electromagnetic relay which can solve the above-mentioned problems, the inventors of the present application has previously proposed the following electromagnetic relay (see Japanese laid-open Patent Publication No. 162712/1998).
The previously-proposed electromagnetic relay comprises a main body assembly, formed by combining an electromagnet assembly comprising a coil assembly comprising of a spool and coils wound around the spool and an iron core and a yoke with a movable contact and an armature, and a terminal board assembly having fixed contact terminal attached to a terminal board. These main body assembly and terminal board are separate members and engage with each other to comprise an electromagnetic relay.
FIGS. 1A to 1D of the accompanying drawings are diagrams to which reference will be made in explaining the outline of this previously-proposed electromagnetic relay. In the electromagnetic relay of this example, a main body assembly 1 shown in FIG. 1A and a terminal board assembly 2 shown in FIG. 1B are assembled to form an electromagnetic relay main body 3 shown in FIG. 1D.
In the example shown in FIGS. 1A to 1D, the electromagnetic relay main body 3 is formed by assembling the two members of the main body assembly 1 and the terminal board assembly 2. The electromagnetic relay main body 3 is housed within a cover 4 shown in FIG. 1C. Then, a sealant seals the opening portion of the cover 4 to complete the electromagnetic relay.
The main body assembly 1 comprises an electromagnet assembly 20 and an armature assembly 30. The electromagnet assembly 20 comprises a coil assembly 10 and an iron core (not shown) and a yoke 21, both of which are attached to the coil assembly 10. The coil assembly 10 comprises a resin spool 11 including square plate-like flange portions 11a and 11b provided at respective ends thereof, a coil 13 wound around the spool 11 and coil terminals 12a and 12b, made of copper alloys, for example, attached thereof.
The flange portion 11a has a projection portion 11c projecting in the direction perpendicular to the plane of the plate thereof. This projection portion 11c serves as an engagement portion when the coil assembly 10 is fitted into the terminal board assembly 2. The flange portion 11b has a projection portion 11d serving as an engagement portion when the coil assembly 10 is fitted into the terminal board assembly 2, as will be described later on. The projection portion 11d projects from the upper surface of the flange portion 11b to the direction parallel to the central axis direction of the coil winding portion.
The armature assembly 30 comprises a substantially L-like movable contact spring 31 made of a copper alloy, for example, and a square plate-like armature 32 made of steel attached to the movable contact spring 31.
The terminals strip assembly 2 includes a terminal board 40 shown in FIG. 2A into which a make fixed contact terminal 50 shown in FIG. 2B and a break fixed contact terminal 60 are fitted and is shaped as shown in FIG. 2D.
The terminal board 40 is made of resin and shaped like a thin plate by molding. Specific shape and structure of the terminal board 40 will be described with reference to FIGS. 3A to 3I and FIGS. 4A and 4B.
FIG. 3A is a front view showing the terminal board 40 from a surface 40a of the side from which the make fixed contact terminal 50 and the break fixed contact terminal 60 are fitted into the terminal board 40 (i.e. opposite side of a surface 40b shown in FIG. 2A). FIG. 3B is a side view of the terminal board 40, and FIG. 3C is a top view of the terminal board 40.
FIG. 3D is a cross-sectional view taken along the line Dxe2x80x94D in FIG. 3A. FIG. 3E is a cross-sectional view taken along the line Exe2x80x94E in FIG. 3A. FIG. 3F is a cross-sectional view taken along the line Axe2x80x94A in FIG. 3A. FIG. 3G is a cross-sectional view taken along the line Bxe2x80x94B in FIG. 3A. FIG. 3H is a cross-sectional view taken along the line Cxe2x80x94C in, FIG. 3A. FIG. 3I is a cross-sectional view taken along the line Fxe2x80x94F in FIG. 3B.
FIG. 4B is a diagram showing the terminal board 40 from the side of the surface 40b in which the terminal board 40 is fitted into the main body assembly 1. FIG. 4A is a cross-sectional view taken along the line Gxe2x80x94G in FIG. 4B.
As shown in FIG. 3A, the terminal board 40 is provided with engagement recesses 41, 42, 43, 44, 45. Into the engagement recesses 41, 42, 43, 44, 45, there are fitted engagement projection plates, which will be described later on, formed on the make fixed contact terminal 50 and the break fixed contact terminal 60. The engagement recesses 41, 42, 43, 44, 45 are dead recesses as shown in FIGS. 3D, 3E, 3F, 3G, 3H. In the case of this example, the engagement recesses 41 and 44 serve to engage the make fixed contact terminal 50 with the terminal board 40 and the engagement recesses 42, 43 and 45 serve to engage the break fixed contact terminal 60 with the terminal board 40.
The terminal board 40 has, at its surface 40b side, engagement portions which are engaged with the main body assembly 1. Specifically, the terminal board 40 has at its surface 40b side recesses 46a, 46b in which there is disposed the portion of the coil 13 of the main body assembly 1. Further, as shown in FIG. 3G and FIGS. 4A, 4B, the terminal board 40 has at its surface 40b side a recess 47 into which there is fitted the projection portion 11d formed on the flange portion 11b of the coil 11 shown in FIG. 1A.
A height h of the major plate portion of the terminal board 40 is shorter than a height of the spool 11 (length from the bottom portion of the flange portion 11c to the upper surface of the flange portion 11b). Therefore, as will be described later on, the major plate portion in which the engagement recesses 41 to 45 are formed on the terminal board 40 may be inhibited from being located around the portion in which the movable contact and the fixed contacts are located.
Then, the terminal board 40 has a projection portion 48 projecting from the major plate portion to the plane direction of the plate portion. The recess portion 47 is formed on this projection portion 48.
The terminal board 40 has, at its surface 40b side, an engagement projection member 49 including a through-hole 49a which is fitted with the projection portion 11c formed on the flange portion 11a side of the spool 11. This engagement projection member 49 is a thin U-like plate member projecting from the bottom portion 40c of the terminal board 40 in the height direction to the direction perpendicular to the plane of the plate of the terminal board 40. The engagement projection member 49 can deviate in the plate thickness direction of the engagement projection member 49 relative to the terminal board 40 under spring force.
Further, the terminal board 40 has, at its surface 40b side, a recess portion 40d which is flush with the upper surface of the engagement projection member 49 as shown in FIGS. 3F, 3G, 3H and 3I. The recess portion 40d accepts a coil end connection portion of a coil terminal to which a winding start end and a winding ending end of the coil 13 are connected when the main body assembly 1 is fitted into the terminal board assembly 2.
The make fixed contact terminal 50 and the make fixed contact terminal 60 which are engaged to the terminal board 40 will be described more in detail with reference to FIGS. 5A, 5B, 5C and FIGS. 6A, 6B, 6C.
Specifically, FIGS. 5A, 5B, 5C are a top view, a front view and a side view of the make fixed contact terminal 50, respectively. FIGS. 6A, 6B, 6C are a top view, a front view and a side view of the break fixed contact terminal 60, respectively.
As shown in FIGS. 5A to 5B and FIGS. 6A to 6C, the make fixed contact terminal 50 and the break fixed contact terminal 60 include plate portions 50a and 60a which are curved along the plane of the plate of the terminal board 40 when they are fitted into the terminal board 40. The make fixed contact terminal 50 and the break fixed contact terminal 60 have formed thereon external terminal portions 51 and 61 projecting from the bottom portion 40c of the terminal board 40 to the plane direction of the terminal board 40 as extended portions of the plate portions 50a and 60a. 
The plate portions 50a and 60a of the make fixed contact terminal 50 and the break fixed contact terminal 60 have, at their sides opposite to the external terminal portions 51 and 61, plate portions 50a and 60a bent in the direction perpendicular to the plate portions 50a and 60a. The plate portions 50b and 60b include make fixed contacts 52, 53 and break fixed contacts 62, 63.
The plate portions 50a and 60a have, at their intermediate positions between the plate portions 50a and 50b in which the contacts 52, 53 and the contacts 62, 63 are formed and the external terminal portions 51 and 61, engagement projection plate portions 54, 55 and 64, 65, 66 which are fitted into the engagement recesses 41 to 45 of the terminal board 40 with pressure in the direction perpendicular to the plate portions 50a and 60a. 
Then, the engagement projection plate portions 54, 55 of the make fixed contact terminal 50 are fitted into the engagement recess portions 41, 44 of the terminal board 40 with pressure, whereby the make fixed contact terminal 50 is fixed to the terminal board 40. In a like manner, the engagement projection plate portions 64, 65, 66 of the break fixed contact terminal 60 are fitted into the engagement recess portions 42, 43, 45 of the terminal board 40 with pressure, whereby the break fixed contact terminal 60 is fixed to the terminal board 40. FIG. 7 shows the state in which the make fixed contact terminal 50 and the break fixed contact terminal 60 are fixed to the terminal board 40.
As shown in FIG. 7, part of the make fixed contact terminal 50 and part of the break fixed contact terminal 60 cross at the engagement recess portion 44. Since however the engagement projection plate portion 55 of the make fixed contact terminal 50 and which engages with the engagement recess portion 44 is shaped as U-like plate portion as shown in FIG. 2B and the corresponding portion of the plate portion 50b of the make fixed contact terminal 50 is recessed as shown in FIGS. 2B and 5A, the make fixed contact terminal 50 and the break fixed contact terminal 60 are not in contact with each other and are electrically separated from each other.
The make fixed contacts 52, 53 and the break fixed contacts 62, 63 are spaced apart from each other by a predetermined distance as shown in FIGS. 2D and 7. A distance h2 (see FIG. 5B) ranging from the position of the engagement projection plate portion 55 of the make fixed contact terminal 50 to the plate portion 50 in which the make fixed contacts 52, 53 are formed is selected to be larger than a distance h1 (see FIG. 3A) ranging from then position of the engagement recess portion 44 of the terminal board 40 to an end edge 40e of the major plate portion in the height direction, except the projection portion 48 of the terminal board 40 (h1 less than h2). As a consequence, the plate portion 50b of the make fixed contact terminal 50 and the end edge 40e of the major plate portion of the terminal board 40 are distant from each other along the height direction of the terminal board 40.
Consequently, the portion of the terminal board 40 made of resin except the projection portion 48 does not exist near the positions of the heights of the make fixed contacts 52, 53 and the break fixed contacts 62, 63. That is, even when the excess current flows through the movable contact and the make fixed contacts 52, 53 to produce heat in the coil during the electromagnetic relay is operating, the resin of the terminal board 40 hardly exists near the contact portions so that the movable contact and the make fixed contacts 52, 53 can be prevented from fixedly adhering.
Moreover, when the make fixed contact terminal 50 and the break fixed contact terminal 60 are fitted into the terminal board 40 with pressure, the engagement projection plate portions 54, 55 and the engagement projection plate portions 64, 65, 66 cut the portions within the engagement recess portions 41 to 45 so that shavings are produced inevitably. However, since the engagement recess portions 41 to 45 are the dead recess portions, the shavings are collected into the engagement recess portions 41 to 45 so that they can be prevented from being scattered to the outside. Therefore, there can be removed a risk that shavings are attached to the contact portions to cause contact failures.
When the movable contact is alternately switched to the make fixed contacts and the break fixed contacts, it is unavoidable that metal shavings are scattered due to butting and abrasion of contact metals. If metal plate portions of a plurality of fixed contact terminals are not exposed to the outside, or if a plurality of fixed contact terminals has sufficiently large spaces, there is then no risk that the above-mentioned metal shavings will short-circuit a plurality of fixed contact terminals.
However, in the case of the above-mentioned electromagnetic relay, as shown in FIG. 7, the make fixed contact terminal 50 and the break fixed contact terminal 60 are exposed to the side of one surface 40a of the terminal board 40 and the metal plate surfaces of the make fixed contact terminal 50 and the break fixed contact terminal 60 are brought in close contact with this surface 40a. 
As a result, when the spacing between the metal plate portions of the make fixed contact terminal 50 and the break fixed contact terminal 60 is small, the above-mentioned metal shavings are accumulated in the gap space. There is a risk that the make fixed contact terminal 50 and the break fixed contact terminal 60 will be short-circuited.
In view of the aforesaid aspect, it is an object of the present invention to provide an electromagnetic relay in which problems caused by metal shavings produced when metal contacts are connected can be avoided.
According to an aspect of the present invention, there is provided an electromagnetic relay in which an electromagnetic relay main body having a plate portion made of an insulating material with a plurality of fixed contact terminals attached thereto is inserted into a cover. The plate portion includes a first engagement portion located at the position in which said plurality of fixed contact terminals are isolated from each other. And the cover includes a second engagement portion that engages with the first engagement portion at an inner wall surface to which the plate portion opposes when the electromagnetic relay main body is inserted into the cover.
According to the above-mentioned arrangement, in the electromagnetic relay in which the electromagnetic relay main body is inserted into the cover, respective metal plate portions of a plurality of fixed contact terminals fixed to the plate portion made of an insulating material are isolated by the engagement portion of the terminal board and the second engagement portion of the cover from a space standpoint.
Therefore, it can avoided such an accident in which metal shavings produced when the movable contact contacts with the fixed contact will fuse the metal plate portions of a plurality of fixed contact terminals to short-circuit a plurality of fixed contact terminals.